The long term goal of this project is to determine at a molecular level the structural basis for the known physiological function and mechanism of action of Transferrin (Tf). We hope to achieve this through comprehensive crystallographic studies on Tf. The specific aims of this proposal are tri-phasic. The first phase involves the determination of the structure of iron-saturated chicken ovo-Tf to a resolution of 3.5-3.0 A and of the homologous apo-Tf to a resolution of 6.5-6.0 A. This will be carried out using single crystal X-ray diffraction methods, as these have been applied to protein structures. The second phase is on studies on the structure of abortive complexes of Tf i.e., complexes with metals other than iron and anions other than carbonate. The third phase will concern itself with attempts at crystallization as well as preliminary studies of Tf from diverse sources.